Reflective polarizer and display system including the same

Abstract

To provide a reflective polarizer that provides low color shift with a viewing angle that is robust against manufacturing variations, while allowing a high transmittance of infrared light from an infrared light source.SOLUTION: A reflective polarizer has a transmittance for a first polarization state having a band edge separating a first wavelength range extending at least from about 450 nm to about 900 nm and a second wavelength range extending at least from about 1100 nm to about 1300 nm. For the first polarization state, the reflective polarizer has an average transmittance in the first wavelength range less than about 10% and an average transmittance in the second wavelength range greater than about 80%, and for a second polarization state, the reflective polarizer has an average transmittance in the first wavelength range greater than about 40% and an average transmittance in the second wavelength range greater than about 80%. A display system includes the reflective polarizer and an infrared light source configured to emit infrared light having a wavelength W1. The band edge has a band edge wavelength of W2>W1.SELECTED DRAWING: Figure 1A

Description

[Background technology]

[0001] A display system, such as a liquid crystal display system, can include a reflective polarizer, which can be a collimating reflective polarizer.

[0002] The display system may include an infrared light source and sensor for fingerprint detection. Summary of the Invention

[0003] This description generally relates to a reflective polarizer and a display system. The reflective polarizer can be a collimating reflective polarizer that has higher transmittance for normally incident light than for obliquely incident light. The display system can include the reflective polarizer, a display panel, and an infrared light source. The reflective polarizer can be configured to provide low color shift with viewing angle that is robust to manufacturing variations while enabling high transmittance of infrared light from the infrared light source.

[0004] According to some aspects of the present disclosure, a display system for detecting a user's finger is provided. The display system includes a display panel configured to generate an image for viewing by a user, a sensor for detecting the user's finger disposed proximate to the display panel, an infrared light source configured to emit infrared light having a wavelength W1 toward the user's finger, and a reflective polarizer disposed between the display panel and the sensor. The sensor is configured to receive and detect at least a portion of the infrared light reflected by the finger. For substantially normally incident light and a first polarization state, the optical transmittance of the reflective polarizer includes a first band edge separating a first wavelength range and a second wavelength range, the first wavelength range extending from at least about 450 nm to about 900 nm and the second wavelength range extending from at least about 1100 nm to about 1300 nm. For substantially normally incident light and for a first polarization state, the reflective polarizer has an average light transmittance of less than about 10% within a first wavelength range and an average light transmittance of greater than about 80% within a second wavelength range. For substantially normally incident light and for a second polarization state orthogonal to the first polarization state, the reflective polarizer has an average light transmittance of greater than about 40% within the first wavelength range and an average light transmittance of greater than about 80% within the second wavelength range. In some embodiments, the first band edge has a band edge wavelength W2 corresponding to about 50% light transmittance along the first band edge, where W2>W1. In some such embodiments, or in other embodiments, W1<975 nm, and the reflective polarizer is configured such that, for substantially white incident light and for a second polarization state, the maximum difference in color between the light transmitted through the reflective polarizer and the incident light is less than or equal to about 0.07 in CIE 1931 xy color space as the angle of incidence of the incident light varies from 0 degrees to about 60 degrees in each of a plane of incidence parallel to the second polarization state and a plane of incidence orthogonal to the second polarization state.

[0005] According to some embodiments of the present disclosure, there is provided a reflective polarizer including a plurality of alternating polymer layers, totaling at least 10, each polymer layer having an average thickness of less than about 500 nm. For substantially perpendicularly incident light and for a first polarization state, the reflective polarizer has an average light transmittance of less than about 5% within a first wavelength range spanning from about 425 nm to about 650 nm. For substantially perpendicularly incident light and for a second polarization state orthogonal to the first polarization state, the reflective polarizer has an average light transmittance T1 of greater than about 40% within the first wavelength range. For light incident on the reflective polarizer at an angle of incidence of about 60 degrees, and for the first polarization state and a plane of incidence parallel to the first polarization state, the reflective polarizer has an average light transmittance of less than about 5% within the first wavelength range. For light incident on the reflective polarizer at an angle of incidence of about 60 degrees, and for a second polarization state and a plane of incidence parallel to the second polarization state, the optical transmittance of the reflective polarizer has a first band edge separating a first wavelength range from a second wavelength range spanning at least about 850 nm to about 1100 nm, and a best linear fit correlating optical transmittance to wavelength over at least the wavelength range in which optical transmittance increases from about 20% to about 80% relative to the first band edge has a slope greater than about 3% / nm and an r-squared value greater than about 0.9, and a best second-order polynomial fit to the optical transmittance in the first wavelength range has a negative second-order coefficient and an r-squared value greater than about 0.9. For light incident on the reflective polarizer at an angle of incidence of about 60 degrees, and for a second polarization state and a plane of incidence parallel to the second polarization state, the reflective polarizer has an average light transmission T2 within a first wavelength range of about 15% to about 35% and an average light transmission greater than about 80% within a second wavelength range, where T1-T2≧10%.

[0006] These and other aspects will become apparent from the following detailed description. In no event, however, should this brief summary be construed as limiting the claimed subject matter. [Brief explanation of the drawings]

[0007] [Figure 1A] 1 is a schematic cross-sectional view of an exemplary display system. [Figure 1B] 1 is a schematic cross-sectional view of an exemplary display system. [Figure 2] 1 is a schematic cross-sectional view of an exemplary sensor. [Figure 3] 1 is a schematic plot of transmission versus wavelength through an exemplary optical filter. [Figure 4] 1 is a schematic plot of emission versus wavelength from an infrared light source. [Figure 5A] 1 is a schematic cross-sectional view of an exemplary extended illumination source. [Figure 5B] 1 is a schematic cross-sectional view of an exemplary extended illumination source. [Figure 6] 1 is a schematic cross-sectional view of an exemplary reflective polarizer. [Figure 7] 1 shows the layer thickness profile of an exemplary reflective polarizer. [Figure 8A] FIG. 1 is a schematic diagram of an incident plane. [Figure 8B] FIG. 1 is a schematic diagram of an incident plane. [Figure 9] 1 is a plot of the transmission of an exemplary reflective polarizer for various polarization states and angles of incidence. [Figure 10] 1 is a plot of the transmission of an exemplary reflective polarizer for angles of incidence of 20 degrees and 60 degrees. [Figure 11] 1 is a plot of the band edges of an exemplary reflective polarizer for a 60 degree angle of incidence. [Figure 12] 1 is a plot of the band edges of an exemplary reflective polarizer for normally incident light. [Figure 13] 1 is a plot of the transmission of an exemplary reflective polarizer for an incident angle of 60 degrees. [Figure 14] 1 shows a schematic representation of color shift due to angle of incidence in the CIE xy color space. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various embodiments. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0009] According to some embodiments herein, a display system includes a reflective polarizer having a band edge wavelength greater than the wavelength of infrared light used in the display system to sense a user's finger applied to the display system (e.g., to detect fingerprints). Reflective polarizers used in display systems with finger sensors have traditionally been selected to have a band edge below the wavelength of infrared light used for finger sensing. However, this can cause undesirable color shifts at high viewing angles (e.g., greater than about 60 degrees) due to manufacturing variations that shift the band edge to a wavelength low enough for some regions of the film to significantly affect the color shift. Furthermore, having a band edge below the wavelength of infrared light can result in undesirable color shifts at very high viewing angles (e.g., greater than about 75 degrees), even in the absence of manufacturing variations. Moving the band edge to a higher wavelength can reduce or eliminate the areas of the film that result in undesirable color shifts, but results in reduced transmission of infrared light in conventional display systems. According to some embodiments herein, a display system can be configured such that infrared light is incident on a reflective polarizer at an oblique angle of incidence, resulting in a band edge of the reflective polarizer shifting below infrared wavelengths at oblique angles of incidence. This allows for reduced color shift with viewing angle, even with manufacturing variations and / or for very high viewing angles, without substantially reducing the transmission of infrared light through the reflective polarizer. Furthermore, according to some embodiments, the reflective polarizer has a transmission spectrum shaped to further reduce color shift with viewing angle for obliquely incident light.

[0010] 1A-1B are schematic cross-sectional views of a display system 1000, 1000′ for sensing a finger 180 of a user 190 applied to the display system 1000, 1000′, according to some embodiments. The display system 1000, 1000′ includes a display panel 110 configured to generate an image 112 for viewing by the user 190, a sensor 120 for sensing the finger 180 of the user 190 positioned proximate the display panel 110, an infrared light source 125 configured to emit infrared light 127 having a wavelength W1 (see, for example, FIGS. 3 and 9 ) toward the finger 180 of the user 190, the sensor 120 configured to receive and detect at least a portion of the infrared light 127 reflected by the finger 180, and a reflective polarizer 200 positioned between the display panel 110 and the sensor 120 such that the reflective polarizer 200 has any of the transmittance characteristics described elsewhere herein. For example, in some embodiments, for substantially perpendicularly incident light, for a first polarization state, the light transmittance of the reflective polarizer has a first band edge separating a first wavelength range and a second wavelength range, the first wavelength range spanning at least about 450 nm to about 900 nm and the second wavelength range spanning at least about 1100 nm to about 1300 nm, and the reflective polarizer has an average light transmittance of less than about 10% within the first wavelength range and an average light transmittance of greater than about 80% within the second wavelength range; and for a second polarization state orthogonal to the first polarization state, the reflective polarizer has an average light transmittance of greater than about 40% within the first wavelength range and an average light transmittance of greater than about 80% within the second wavelength range. In some embodiments, for substantially perpendicular incident light and for a first polarization state, the reflective polarizer 200 has a first band edge separating a first wavelength range and a second wavelength range, and has a band edge wavelength W2 corresponding to approximately 50% light transmission along the first band edge.In some embodiments, the reflective polarizer 200 is configured so that, for substantially white incident light and a second polarization state, the maximum difference in color between the light transmitted through the reflective polarizer and the incident light is about 0.07 or less in the CIE 1931 xy color space as the angle of incidence (angle relative to the surface normal) of the incident light varies from 0 degrees to about 60 degrees in each of the planes of incidence parallel to the second polarization state (the plane defined by the direction of light propagation and the surface normal) and orthogonal to the second polarization state. In some embodiments, W2>W1.

[0011] In some embodiments, infrared light 127 initially enters the reflective polarizer at an angle of incidence θ1 greater than about 40 degrees (e.g., in a range of about 40 degrees to about 80 degrees, or about 45 degrees to about 70 degrees). In some embodiments, sensor 120 is positioned to receive light that is reflected from the finger and then enters the reflective polarizer at an angle of incidence θ2 greater than about 40 degrees (e.g., in a range of about 40 degrees to about 80 degrees, or about 45 degrees to about 70 degrees). For display system 1000, infrared light 127 transmits through reflective polarizer 200, reflects from finger 180, transmits back through reflective polarizer 200, and is then received by sensor 120. For display system 1000′, infrared light 127 initially transmits to finger 180 without transmitting reflective polarizer 200, then reflects from finger 180, transmits through reflective polarizer 200, and is then received by sensor 120. In this case, infrared light 127 first strikes the reflective polarizer 200 at an angle of incidence θ2. In some embodiments, the display system includes a cover glass 111, and the display panel 110 is disposed between the cover glass 111 and the reflective polarizer 200.

[0012] 2 is a schematic cross-sectional view of sensor 120 according to some embodiments. Sensor 120 may be an infrared sensor sensitive to wavelength W1. Sensor 120 includes sensor 120′ and may further include wavelength-selective optical filter 122 and / or angle-selective optical filter 126. Alternatively, optical filters 122 and / or 126 may be considered separate elements disposed on or proximate to the sensor. Optical filter 122 may be disposed between optical filter 126 and sensor 120′, or optical filter 126 may be disposed between optical filter 122 and sensor 120′. Optionally, one or both of optical filters 126 and 122 may be omitted. Sensor 120′ may be or include, for example, a photodiode. In some embodiments, sensor 120 includes an angle-selective optical filter 126 adapted to substantially transmit light 227 incident on the sensor at an oblique angle of incidence and substantially block light 229 incident normally on the sensor. In some such embodiments, or in other embodiments, sensor 120 includes a wavelength-selective optical filter 122 that substantially transmits wavelength W1 and substantially blocks visible and / or near-infrared wavelengths more than 100 nm greater than W1. The angle-selective optical filter 126 can include an array of microlenses and an optically opaque mask layer having through-holes (e.g., pinholes) therein, the through-holes being in one-to-one correspondence with the microlenses and offset (along the mask layer) relative to the microlenses such that the optical filter 126 primarily transmits obliquely incident light. Such optical filters are known in the art and are described, for example, in WO 2020 / 035768 (Yang et al.). The wavelength-selective optical filter 122 may include a layer having dyes and / or pigments and / or may include an interference filter.

[0013] 3 is a schematic plot of transmittance through optical filter 122, according to some embodiments. In some embodiments, optical filter 122 includes a passband 123 having a full width at half maximum 124 of less than about 100 nm, or less than about 80 nm. In some embodiments, optical filter 122 substantially transmits wavelength W1 and substantially blocks wavelength W2.

[0014] 4 is a schematic plot of emission 161 from infrared light source 125 versus wavelength. Emission 161 has a peak 162 at peak emission wavelength 163. The wavelength W1 of the light emitted by the infrared light source can be peak emission wavelength 163. In some embodiments, emission 161 has a full width at half maximum of less than about 20 nm, or less than about 10 nm, or less than about 7 nm. In some embodiments, infrared light source 125 is, for example, a laser diode. In some embodiments, infrared light source 125 is a near-infrared light emitting diode.

[0015] In some embodiments, the display panel 110 is a liquid crystal display panel. Such display panels typically utilize an extended illumination source (e.g., a backlight) to provide light to the display panel. In some embodiments, the display system 1000, 1000′ includes an extended illumination source 114, and the reflective polarizer 200 is disposed between the extended illumination source 114 and the display panel 110. In some embodiments, the reflective polarizer 200 is a collimating reflective polarizer. Such a polarizer can provide a collimating effect by reflecting light with larger angles of incidence back toward the extended illumination source 114 so that the light is recycled. Liquid crystal displays (LCDs) often include brightness-enhancing prism films (typically crossed prism films) to improve the on-axis brightness of the display. In some cases, such films can be omitted when a collimating reflective polarizer is included. In some embodiments of the display system 1000, 1000', there is no brightness-enhancing prism film disposed between the display panel 110 and the back reflector of the extended illumination source 114 (e.g., reflector 117 shown in Figures 5A-5B).

[0016] 5A-5B are schematic cross-sectional views of extended illumination sources 214 and 214′, respectively, either of which may correspond to extended illumination source 114 according to some embodiments. In some embodiments, extended illumination source 214 includes a light guide 113, at least one light source 119, and a reflector 117, where light guide 113 is disposed between reflector 117 and reflective polarizer 200. The at least one light source 119 may be multiple light sources (e.g., light emitting diodes) disposed along an end or ends of light guide 113. In some embodiments, extended illumination source 214′ includes a reflector 117 and an optical diffuser 182 adjacent to reflector 117, where optical diffuser 182 and reflector 117 are substantially coextensive in length and width and define an optical cavity 188 therebetween, with at least one light source 119 disposed within the optical cavity.

[0017] Layers or elements may be described as being substantially coextensive in length and width with one another if at least about 60% of the length and width of each layer or element is coextensive with at least about 60% of the length and width of each other layer or element. In some embodiments, when layers or elements are described as being substantially coextensive in length and width with one another, at least about 80% or at least about 90% of each layer or element is coextensive in length and width with at least about 80% or at least about 90% of the length and width of each other layer or element.

[0018] FIG. 6 is a schematic cross-sectional view of a reflective polarizer 200 according to some embodiments, including a plurality of alternating polymer layers 141, 142, which may total at least 10 or at least 100, each having an average thickness of less than about 500 nm. The reflective polarizer may also include other layers (e.g., skin layer(s) or protective boundary layer(s)) having thicknesses greater than about 500 nm, or greater than about 1 micrometer, or greater than about 2 micrometers. The number of layers 141, 142 may significantly exceed that shown schematically in FIG. 6. In some embodiments, the total number of alternating polymer layers 141, 142 is in the range of 500 to 1200. The transmission spectrum of the reflective polarizer 200 may be specified for orthogonal first (e.g., block) and second (e.g., pass) polarization states 151, 152, respectively, for substantially normally incident light 150. Alternatively or additionally, the transmission spectrum may be specified for p-polarized (polarized in the plane of incidence) and / or s-polarized (polarized orthogonal to the plane of incidence) light at oblique angles of incidence, as further described elsewhere herein.

[0019] As is known in the art, multilayer optical films, such as reflective polarizer films, containing alternating polymer layers can be used to provide desired reflectance and transmittance in a desired wavelength range by appropriately selecting layer thicknesses and refractive index differences. Multilayer optical films and methods for making multilayer optical films are described, for example, in U.S. Patent Nos. 5,882,774 (Jonza et al.), 6,179,948 (Merrill et al.), 6,783,349 (Neavin et al.), 6,967,778 (Wheatley et al.), and 9,162,406 (Neavin et al.). Reflective polarizers with sharp band edges are known in the art and are described, for example, in U.S. Patent No. 6,967,778 (Wheatley et al.). In some embodiments, the reflective polarizer 200 is a collimating reflective polarizer. Collimating reflective polarizers are known in the art and are described, for example, in U.S. Pat. Nos. 9,441,809 (Nevitt et al.) and 9,551,818 (Weber et al.). Suitable materials for the reflective polarizers herein include the polymers described in these references. For example, the reflective polarizer may include alternating substantially isotropic low refractive index layers (e.g., amorphous polyester) and oriented high refractive index layers (e.g., birefringent naphthalene-based polyester).

[0020] FIG. 7 is a plot of the layer thickness profile of an exemplary reflective polarizer. The layer thickness profile refers to layer thickness versus layer number when the alternating polymer layers 141, 142 are numbered sequentially from one side of the reflective polarizer to the other. Layer thickness profiles of narrower and broader band reflective polarizers are shown. The narrower band reflective polarizer included a total of 650 alternating polymer layers 141, 142 and had a band edge wavelength of 901 nm for the first (e.g., blocking) polarization state 151 for substantially perpendicular incident light 150. The broader band reflective polarizer included a total of 850 alternating polymer layers 141, 142 and had a band edge wavelength of 986 nm for the first (e.g., blocking) polarization state 151 for substantially perpendicular incident light 150.

[0021] In some embodiments, the layer thickness profile is selected to provide a transmission spectrum that includes a concave downward portion within the visible or visible-near-infrared wavelength range and a sharp band edge separating the visible or visible-near-infrared wavelength range from the near-infrared range. In some embodiments, the layer thickness profile increases substantially monotonically from the thinnest polymer layer adjacent one side of the reflective polarizer to the thickest polymer layer adjacent the opposite side of the reflective polarizer, and the layer thickness profile has a generally concave downward shape, as shown in FIG.

[0022] 8A-8B are schematic diagrams of light incident on the reflective polarizer 200 at different planes of incidence. Light 150 is incident on the reflective polarizer 200 substantially normal to the polarizer, and light 159, 159' are incident on the polarizer 200 at an angle of incidence θ. In FIG. 8A, light 159 is incident on the polarizer 200 at a plane of incidence parallel to the xz plane, while in FIG. 8B, light 159' is incident on the polarizer 200 at a plane of incidence parallel to the yz plane. The first polarization state 151 can be described as the polarization state in which the electric field projected onto the plane of the reflective polarizer 200 (the xy plane) is along the block axis (x-axis), and the second polarization state 152 can be described as the polarization state in which the electric field projected onto the plane of the reflective polarizer 200 (the xy plane) is along the pass axis (y-axis). In the xz plane of incidence (FIG. 8A), the first polarization state 151 is a p-polarization state and the second polarization state 152 is an s-polarization state. In the yz plane of incidence (FIG. 8B), the first polarization state 151 is an s-polarization state and the second polarization state 152 is a p-polarization state.

[0023] FIG. 9 is a plot of the transmittance of an exemplary reflective polarizer for various polarization states and angles of incidence. T0 cutoff and T0 pass indicate the transmittance for normally incident light having a first polarization state (151) and a second polarization state (152), respectively. Tp60 cutoff and Ts60 cutoff indicate the transmittance for light incident on the reflective polarizer at a 60-degree angle of incidence in a first polarization state 151, with the plane of incidence parallel and perpendicular to the first polarization state 151, respectively. Tp60 pass and Ts60 pass indicate the transmittance for light incident on the reflective polarizer at a 60-degree angle of incidence in a second polarization state 152, with the plane of incidence parallel and perpendicular to the second polarization state 152, respectively. The reflective polarizer in FIG. 9 used the layer thickness profile shown in FIG. 7 for the broader band case. The transmission spectrum of a reflective polarizer using the layer thickness profile shown in FIG. 7 for the narrower band case appears similar, but the band edges are shifted to lower wavelengths. The transmission spectrum shown in Figure 9 was calculated using conventional optical modeling techniques. The alternating layers 141, 142 were modeled as including low-index layers of amorphous polyester (glycol-modified polyethylene terephthalate (PETg)) and high-index layers of oriented polyethylene naphthalate (PEN). The low-index layers were modeled as isotropic, with a refractive index of 1.563 at 633 nm, and the high-index layers were modeled as having refractive indices of 1.804 in the x-direction, 1.615 in the y-direction, and 1.51 in the z-direction at 633 nm. The reflective polarizer was modeled as including 500 nm thick PETg skin layers on each side of the reflective polarizer.

[0024] The optical transmittance 210 of FIG. 9 includes band edges 212 and 222. One of the band edges 212 and 222 may be referred to as the first band edge, and the other of the band edges 212 and 222 may be referred to as the second band edge. In some embodiments, for substantially normally incident light 150 and a first polarization state 151, the optical transmittance 210 of the reflective polarizer 200 has a first band edge 212 separating a first wavelength range and a second wavelength range, where the first wavelength range extends from at least about 450 nm to about 900 nm and the second wavelength range extends from at least about 1100 nm to about 1300 nm. The first band edge 212 has a band edge wavelength W2 corresponding to approximately 50% optical transmittance along the first band edge 212. For substantially normally incident light 150 and a first polarization state 151, the reflective polarizer 200 has an average light transmittance of less than about 10% within a first wavelength range and an average light transmittance of greater than about 80% within a second wavelength range. For substantially normally incident light 150 and a second polarization state 152 that is orthogonal to the first polarization state 151, the reflective polarizer has an average light transmittance of greater than about 40% within the first wavelength range and an average light transmittance of greater than about 80% within the second wavelength range. In some embodiments, for substantially normally incident light 150 and the second polarization state 152, the reflective polarizer has an average light transmittance of about 50% to about 70% within a wavelength range from about 450 nm to about 650 nm. In some embodiments, the average light transmission of the reflective polarizer 200 within the first wavelength range for substantially normally incident light 150 and for the first polarization state 151 is less than about 5%, or less than about 3%, or less than about 2%. In some such embodiments, or in other embodiments, the average light transmission within the second wavelength range for substantially normally incident light 150 and for the first polarization state 151 is greater than about 85% or greater than about 90%.

[0025] In some embodiments, the first wavelength range spans from at least about 450 nm to about 925 nm, or to about 940 nm, or to about 950 nm. In some embodiments, the first wavelength range spans from at least about 425 nm to about 900 nm, or to about 925 nm, or to about 940 nm, or to about 950 nm. In some such embodiments, or in other embodiments, the second wavelength range spans from at least about 1100 nm to about 1350 nm, or at least about 1050 nm to about 1350 nm.

[0026] The wavelength W1 of the infrared light 127 emitted by the infrared light source 125 is shown in FIG. 9 as the full width at half maximum 124 of the passband of the optical filter 122. In some embodiments, W1<975 nm, or W1<960 nm, or W1<950 nm. In some embodiments, W2>W1. In some embodiments, W2-W1>10 nm, or W2-W1>20 nm, or W2-W1>30 nm. In some such embodiments, or in other embodiments, W2>960 nm and W1<950 nm.

[0027] 10 is a plot of the transmittance of the reflective polarizer of FIG. 9 for p-polarization states and angles of incidence of 20 degrees and 60 degrees. Tp20 Pass and Tp60 Pass represent the transmittance of light incident on the reflective polarizer at angles of incidence of 20 degrees and 60 degrees, respectively, relative to second polarization state 152 and a plane of incidence parallel to second polarization state 152. In some embodiments, for second polarization state 152 and a plane of incidence parallel to second polarization state 152, and for a wavelength range spanning at least about 450 nm to about 650 nm, the reflective polarizer has a greater average optical transmittance Tpθ1 for light incident at smaller angles of incidence (e.g., 20 degrees, or 10 degrees, or 5 degrees) and a smaller average optical transmittance Tpθ2 for light incident at larger angles of incidence (e.g., 40 degrees, or 50 degrees, or 60 degrees, or 70 degrees). In some embodiments, the difference between the larger average optical transmittance Tpθ1 and the smaller average optical transmittance Tpθ2 is greater than about 20% or greater than about 25%, the smaller angle of incidence is less than about 25 degrees, and the larger angle of incidence is within a range of about 40 degrees to about 70 degrees (e.g., about 60 degrees). In some embodiments, for substantially normally incident light 150 and for the second polarization state 152, the reflective polarizer 200 has an average optical transmittance of about 50% to about 70% within a third wavelength range of about 450 nm to about 650 nm. In some such embodiments, or in other embodiments, for the second polarization state 152 and for light incident on the reflective polarizer at an angle of incidence of about 60 degrees in a plane of incidence parallel to the second polarization state 152, the reflective polarizer has an average optical transmittance within the third wavelength range of about 15% to about 35%, or about 20% to about 30%.

[0028] In some embodiments, for substantially normally incident light 150 and for the second polarization state 152, the reflective polarizer 200 has an average optical transmittance T1 in a third wavelength range extending from about 425 nm to about 650 nm, and for the second polarization state 152 and for light 159′ incident on the reflective polarizer at an incidence angle of about 60 degrees in a plane of incidence parallel to the second polarization state 152, the optical transmittance 210 of the reflective polarizer has a second band edge 222 separating the third wavelength range from a fourth wavelength range extending from at least about 850 nm to about 1100 nm.

[0029] In some embodiments, the optical transmittance 210 includes a generally downwardly concave portion and sharp band edge(s) within the third wavelength range. Such transmission spectra have been found to result in low color shift with viewing angle. FIGS. 11-12 are plots of a portion of the optical transmittance 210, showing band edges 222 and 212, respectively, and best linear fits 224 and 274 to the band edges, respectively. FIG. 13 is a plot of another portion of the optical transmittance 210 for light incident on the reflective polarizer in the second polarization state 152 with a 60-degree angle of incidence and a plane of incidence parallel to the second polarization state 152. In some embodiments, the best linear fit 224 relating the optical transmittance 210 to wavelength, at least over the wavelength range in which the optical transmittance increases from about 20% to about 80% for the second band edge 222, has a slope 226 greater than about 3% / nm and an r-squared value 228 greater than about 0.9. In some embodiments, the best quadratic polynomial fit 234 to the light transmittance 210 in the third wavelength range has a negative quadratic coefficient 235 and an r-squared value 238 greater than about 0.9. In some embodiments, for the second polarization state 152 and for light 159′ incident on the reflective polarizer at an angle of incidence of about 60 degrees with the plane of incidence parallel to the second polarization state 152, the reflective polarizer 200 has an average light transmittance T2 of about 15% to about 35% in the third wavelength range and greater than about 80% in the fourth wavelength range, where T1-T2≧10%, or T1-T2 can be within ranges described elsewhere herein. In some embodiments, the slope 226 is greater than about 3.5% / nm, or greater than about 3.7% / nm. In some such embodiments, or in other embodiments, the r-squared value 228 is greater than about 0.95, or greater than about 0.98.

[0030] In some embodiments, the reflective polarizer 200 includes a plurality of alternating polymer layers 141, 142 totaling at least 10, each polymer layer having an average thickness of less than about 500 nm, such that: For substantially normal incident light, For the first polarization state 151, the reflective polarizer 200 has an average light transmission of less than about 5% within a first wavelength range extending from about 425 nm to about 650 nm; For a second polarization state 152 that is orthogonal to the first polarization state 151, the reflective polarizer 200 has an average light transmission T1 of greater than about 40% within the first wavelength range; For light incident on a reflective polarizer at an angle of incidence of approximately 60 degrees, For a first polarization state 151 and for a plane of incidence parallel to the first polarization state 151 (see, e.g., FIG. 8A ), the reflective polarizer 200 has an average light transmission of less than about 5% within a first wavelength range; For the second polarization state 152 and for a plane of incidence parallel to the second polarization state 152 (see, e.g., FIG. 8B ), the light transmittance 210 of the reflective polarizer 200 has a first band edge 222 separating the first wavelength range from a second wavelength range spanning at least about 850 nm to about 1100 nm, and correlates the light transmittance with wavelength over at least the wavelength range over which the light transmittance increases from about 20% to about 80% relative to the first band edge. The best linear fit 224 has a slope 226 greater than about 3% / nm and an r-squared value 228 greater than about 0.9, the best quadratic polynomial fit 234 to the light transmittance in the first wavelength range has a negative quadratic coefficient 235 and an r-squared value 238 greater than about 0.9, and the reflective polarizer 200 has an average light transmittance T2 of about 15% to about 35% in the first wavelength range and an average light transmittance greater than about 80% in the second wavelength range. In some embodiments, T1 - T2 ≧ 10%.

[0031] In some embodiments, for light incident on the reflective polarizer 200 at an angle of incidence of about 60 degrees in a plane of incidence orthogonal to the first polarization state 151 (e.g., the yz plane), the reflective polarizer 200 has an average light transmittance of less than about 5% within a first wavelength range. In some embodiments, for light incident on the reflective polarizer 200 at an angle of incidence of about 60 degrees in a plane of incidence orthogonal to the second polarization state 152 (e.g., the xy plane), the reflective polarizer 200 has an average light transmittance T3 of about 15% to about 35% within a first wavelength range and an average light transmittance of greater than about 60% within a second wavelength range. In some embodiments, T2 and T3 are each within a range of about 20% to about 30%. In some embodiments, |T3 - T2| ≦8% or |T3 - T2| ≦5%.

[0032] In some embodiments, T1 is in the range of about 50% to about 70%. In some such embodiments, or in other embodiments, T1-T2 ≧15%, or T1-T2 ≧20%, or T1-T2 ≧25%. In some such embodiments, or in other embodiments, T1-T2 ≦60%, or T1-T2 ≦50%, or T1-T2 ≦40%.

[0033] In some embodiments, the first band edge 222 has a first band edge wavelength W3 corresponding to about 50% light transmittance along the first band edge 222, and the first band edge wavelength W3 is at least about 670 nm, or at least about 700 nm, or at least about 720 nm.

[0034] In some embodiments, for substantially normally incident light and for the first polarization state 151, the reflective polarizer 200 has an average light transmission of less than about 3% or less than about 2% within the first wavelength range. In some embodiments, for light incident on the reflective polarizer 200 at an angle of incidence of about 60 degrees, for the first polarization state 151 and a plane of incidence parallel to the first polarization state 151, the reflective polarizer 200 has an average light transmission of less than about 3% or less than about 2% within the first wavelength range. In some embodiments, for substantially normally incident light 150 and for a first polarization state, the optical transmittance 210 of the reflective polarizer 200 has a second band edge 212 separating a third wavelength range and a fourth wavelength range, the third wavelength range spanning at least about 450 nm to about 900 nm and the fourth wavelength range spanning at least about 1100 nm to about 1300 nm, and the reflective polarizer 200 has an average optical transmittance of less than about 5% within the third wavelength range and an average optical transmittance of greater than about 80% within the fourth wavelength range. In some embodiments, for substantially normally incident light 150 and for the first polarization state, the reflective polarizer 200 has an average optical transmittance of less than about 3% or less than about 2% within the third wavelength range. In some embodiments, for substantially normally incident light 150 and for the first polarization state, the reflective polarizer 200 has an average light transmission within the fourth wavelength range of greater than about 85% or greater than about 90%.

[0035] In some embodiments, the third wavelength range spans from at least about 450 nm to about 925 nm, or to about 940 nm, or to about 950 nm. In some embodiments, the third wavelength range spans from at least about 425 nm to about 900 nm, or to about 925 nm, or to about 940 nm, or to about 950 nm. In some such embodiments, or in other embodiments, the fourth wavelength range spans from at least about 1100 nm to about 1350 nm, or at least about 1050 nm to about 1350 nm.

[0036] In some embodiments, for substantially normally incident light 150 and for the second polarization state 152, the reflective polarizer has an average optical transmittance greater than about 80% within the fourth wavelength range. In some embodiments, the second band edge 212 has a second band edge wavelength W2 corresponding to about 50% optical transmittance along the second band edge, the second band edge wavelength W2 being in the range of about 925 nm to about 1050 nm. In some embodiments, a best linear fit 274 correlating optical transmittance to wavelength over at least the wavelength range in which optical transmittance increases from about 10% to about 70% for the second band edge 212 has a slope 276 greater than about 2% / nm and an r-squared value 278 greater than about 0.9. In some embodiments, the slope 226 of the best linear fit 224 to the first band edge 222 is at least about 0.5% / nm, or at least 0.7% / nm, or at least 1% / nm greater than the slope 276 of the best linear fit 274 to the second band edge 212. In some embodiments, the slope 276 is greater than about 2.2% / nm, or greater than about 2.3% / nm. In some such embodiments, or in other embodiments, the r-squared value 278 is greater than about 0.95, or greater than about 0.98.

[0037] In some embodiments, the best quadratic polynomial fit 234 has a positive linear coefficient 236. In some embodiments, the best quadratic polynomial fit 234 has a maximum 239 at a wavelength W4 between about 400 nm and about 550 nm, or between about 425 nm and about 500 nm. In some embodiments, the r-squared value 238 is greater than about 0.95, or greater than about 0.98.

[0038] FIG. 14 is a schematic plot in CIE (Commission Internationale de l'Eclairage) 1931 xy color space showing color shift with angle of incidence θ for light in the second polarization state 152 incident on the reflective polarizer 200. The incident light can be substantially white light, represented by point 333. The substantially white light can have, for example, CIE 1931 x and y coordinates in the ranges of 0.29 to 0.35, or 0.3 to 0.34, respectively. The substantially white light can be, for example, standard illuminant D65, with CIE 1931 x and y coordinates of 0.3127 and 0.329, respectively. The color can shift from point 334, which is closer to point 333 at low or 0-degree angles of incidence, to point 335, which is farther from point 333 at high angles of incidence. In some embodiments, the reflective polarizer 200 is configured such that for substantially white incident light (e.g., represented by point 333) and for the second polarization state 152, the maximum difference in color Δ between the light transmitted through the reflective polarizer and the incident light is about 0.07 or less, or about 0.06 or less, or about 0.05 or less in the CIE 1931 xy color space as the angle of incidence θ of the incident light varies from 0 degrees to about 60 degrees in each of the planes of incidence parallel to the second polarization state 152 and orthogonal to the second polarization state 152. In some embodiments, the reflective polarizer 200 is configured such that, for substantially white incident light and for the second polarization state 152, the maximum difference in color Δ between the light transmitted through the reflective polarizer 200 and the incident light is about 0.08 or less, about 0.07 or less, about 0.06 or less, or about 0.05 or less in the CIE 1931 xy color space as the angle of incidence θ of the incident light varies from 0 degrees to about 75 degrees in each of the planes of incidence parallel to the second polarization state 152 and orthogonal to the second polarization state 152.

[0039] For the reflective polarizer having the transmission spectrum of FIG. 9 , for standard illuminant D65 light and for the second polarization state 152, the calculated color difference Δ between the incident light and the light transmitted through the reflective polarizer for an angle of incidence of 60 degrees was 0.0495 for a plane of incidence parallel to the second polarization state 152 (p-polarized light) and 0.0203 for a plane of incidence orthogonal to the second polarization state 152 (s-polarized light).

[0040] To test the robustness of the low color shift to manufacturing variations that can result in reduced thickness and shifted band edges to lower wavelengths, the color shift was calculated for reflective polarizers with the layer thickness profiles of FIG. 7 corresponding to narrower and wider bands, and for reflective polarizers with thicknesses reduced by 5% or 10%. The incident light had spectra from red, green, and blue light-emitting diodes with relative intensities selected to give CIE 1931 x and y coordinates of 0.3127 and 0.329, respectively. The color shift in CIE 1931 xy color space was calculated for reflective polarizers with reduced thicknesses (95% and 90% thickness) relative to the corresponding reflective polarizers with 100% thickness, for a 60-degree angle of incidence and for the second polarization state 152. For the broader-band reflective polarizer, the color shift was less than 0.044 for 95% and 90% thicknesses and for planes of incidence parallel and orthogonal to the second polarization state 152. For the narrower-band reflective polarizer, the color shift was 0.0924 for 90% thickness and for a plane of incidence orthogonal to the second polarization state 152 (s-polarized light), and 0.1682 for 90% thickness and for a plane of incidence parallel to the second polarization state 152 (p-polarized light). These large color shifts were primarily due to an increase in the CIE x-coordinate, indicating a red shift. The results indicate that the broader-band reflective polarizer provides a low color shift that is more robust to manufacturing variations than that of the narrower-band reflective polarizer.

[0041] The best linear fit described herein can be a linear least squares fit, which is known in the art.The best polynomial fit can also be a least squares fit.Such a fit minimizes the sum of the squares of the residuals, and the residuals are the difference between the data and the fit curve (line or polynomial).By least squares analysis, the r-square value, which is sometimes called the coefficient of determination, can be determined.

[0042] Terms like "about" and the like are used in the context in which they are used and described herein. It will be understood by those of ordinary skill in the art that the use of "about" as applied to quantities expressing feature sizes, quantities, and physical characteristics will mean within 10 percent of the specified value, unless otherwise clear to those of ordinary skill in the art in the context used and described herein. A quantity given as about or approximately a specified value may be exactly that specified value. For example, unless otherwise clear to those of ordinary skill in the art in the context used and described herein, an amount having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and may be 1.

[0043] Terms such as "substantially" are used as they are used and described herein. It will be understood by one of ordinary skill in the art in the context in which it is used and described herein. If the use of "substantially vertical" is not clear to one of ordinary skill in the art in the context used and described herein, "substantially vertical" means within 20 degrees of vertical. An orientation described as substantially vertical may, in some embodiments, be within 10 degrees of vertical, within 5 degrees of vertical, or vertical or nominally vertical.

[0044] All references, patents, or patent applications referenced above are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between any portion of an incorporated reference and this application, the information in the foregoing statement shall prevail.

[0045] Descriptions of elements in the drawings should be understood to apply equally to corresponding elements in other drawings unless otherwise indicated. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that the specific embodiments shown and described may be replaced by various alternative and / or equivalent implementations without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Accordingly, the present disclosure is limited only by the claims and their equivalents.

Claims

1. A display system for detecting a user's finger applied to a display system, comprising: a display panel configured to generate an image for viewing by the user; a sensor disposed adjacent to the display panel for sensing the user's finger; an infrared light source configured to emit infrared light having a wavelength W1 toward the finger of the user, the sensor configured to receive and detect at least a portion of the infrared light reflected by the finger; a reflective polarizer disposed between the display panel and the sensor, for substantially normally incident light: For a first polarization state, the light transmittance of the reflective polarizer includes a first band edge separating a first wavelength range and a second wavelength range, the first wavelength range extending from at least about 450 nm to about 900 nm and the second wavelength range extending from at least about 1100 nm to about 1300 nm, the first band edge having a band edge wavelength W2 corresponding to a light transmittance of about 50% along the first band edge, the reflective polarizer having an average light transmittance of less than about 10% within the first wavelength range and an average light transmittance of greater than about 80% within the second wavelength range, for a second polarization state orthogonal to the first polarization state, the reflective polarizer has an average light transmission greater than about 40% within the first wavelength range and an average light transmission greater than about 80% within the second wavelength range; a reflective polarizer, wherein W2>W1.

2. 10. The display system of claim 1, wherein the sensor is positioned to receive light that is reflected from the finger and then incident on the reflective polarizer at an angle of incidence greater than about 40 degrees.

3. 3. The display system of claim 1, wherein W2>960 nm and W1<950 nm.

4. 4. The display system of claim 1, wherein for the second polarization state and for a plane of incidence parallel to the second polarization state, and for a wavelength range spanning at least about 450 nm to about 650 nm, the reflective polarizer has a greater average light transmittance for light incident at smaller angles of incidence and a lesser average light transmittance for light incident at larger angles of incidence.

5. 5. The display system of claim 4, wherein the difference between the greater average light transmittance and the smaller average light transmittance is greater than about 20%, the smaller angle of incidence is less than about 25 degrees, and the greater angle of incidence is in the range of about 40 degrees to about 70 degrees.

6. for substantially normally incident light and for the second polarization state, the reflective polarizer has an average optical transmittance T1 in a third wavelength range extending from about 425 nm to about 650 nm; 6. The display system of claim 1, wherein the light transmittance of the reflective polarizer includes a second band edge separating the third wavelength range from a fourth wavelength range spanning at least about 850 nm to about 1100 nm, for light incident on the reflective polarizer at an angle of incidence of about 60 degrees with a plane of incidence parallel to the second polarization state, a best linear fit relating the light transmittance to wavelength at least over a wavelength range in which the light transmittance increases from about 20% to about 80% relative to the second band edge has a slope greater than about 3% / nm and an r-squared value greater than about 0.9, and a best quadratic polynomial fit to the light transmittance within the third wavelength range has a negative quadratic coefficient and an r-squared value greater than about 0.9, and the reflective polarizer has an average light transmittance T2 of about 15% to about 35% within the third wavelength range and an average light transmittance greater than about 80% within the fourth wavelength range, and T1-T2≧10%.

7. A display system for detecting a user's finger applied to a display system, comprising: a display panel configured to generate an image for viewing by the user; a sensor disposed adjacent to the display panel for sensing the user's finger; an infrared light source configured to emit infrared light having a wavelength W1 less than 975 nm toward the finger of the user, the sensor configured to receive and detect at least a portion of the infrared light reflected by the finger; a reflective polarizer disposed between the display panel and the sensor, for substantially normally incident light: for a first polarization state, the light transmittance of the reflective polarizer comprises a first band edge separating a first wavelength range and a second wavelength range, the first wavelength range extending from at least about 450 nm to about 900 nm and the second wavelength range extending from at least about 1100 nm to about 1300 nm, the reflective polarizer having an average light transmittance of less than about 10% within the first wavelength range and an average light transmittance of greater than about 80% within the second wavelength range; a reflective polarizer having an average light transmission greater than about 40% in the first wavelength range and greater than about 80% in the second wavelength range for a second polarization state orthogonal to the first polarization state; the reflective polarizer is configured such that, for substantially white incident light and for the second polarization state, a maximum difference in color between light transmitted through the reflective polarizer and the incident light is less than or equal to about 0.07 in CIE 1931 xy color space as the angle of incidence of the incident light varies from 0 degrees to about 60 degrees in each of a plane of incidence parallel to the second polarization state and a plane of incidence orthogonal to the second polarization state.

8. 8. The display system of claim 7, wherein the first band edge has a band edge wavelength W2 corresponding to approximately 50% light transmission along the first band edge, W2 > W1.

9. A reflective polarizer comprising a plurality of alternating polymer layers totaling at least 10, each polymer layer having an average thickness of less than about 500 nm; For substantially normally incident light, For a first polarization state, the reflective polarizer has an average light transmission of less than about 5% within a first wavelength range spanning from about 425 nm to about 650 nm, and for a second polarization state orthogonal to the first polarization state, the reflective polarizer has an average light transmission T1 of greater than about 40% within the first wavelength range, and for light incident on the reflective polarizer at an angle of incidence of about 60 degrees: the reflective polarizer has an average light transmission within the first wavelength range for the first polarization state and for a plane of incidence parallel to the first polarization state of the reflective polarizer of less than about 5%; a best linear fit relating the light transmittance to wavelength over at least a wavelength range in which the light transmittance increases from about 20% to about 80% relative to the first band edge has a slope greater than about 3% / nm and an r-squared value greater than about 0.9; and a best quadratic polynomial fit to the light transmittance in the first wavelength range has a negative quadratic coefficient and an r-squared value greater than about 0.

9. The reflective polarizer of claim 1, wherein the reflective polarizer has an average light transmittance T2 of about 15% to about 35% within the first wavelength range and an average light transmittance greater than about 80% within the second wavelength range, and wherein T1-T2≧10%.

10. 10. The reflective polarizer of claim 9, wherein the first band edge has a first band edge wavelength corresponding to about 50% light transmission along the first band edge, and the first band edge wavelength is at least about 700 nm.

11. 11. The reflective polarizer of claim 9 or 10, wherein the reflective polarizer has an average light transmission T3 of about 15% to about 35% within the first wavelength range and an average light transmission of greater than about 60% within the second wavelength range for light incident on the reflective polarizer at an angle of incidence of about 60 degrees for the second polarization state and in a plane of incidence orthogonal to the second polarization state.

12. 12. The reflective polarizer of claim 11, wherein |T3-T2|≦5%.

13. 13. The reflective polarizer of any one of claims 9 to 12, wherein for substantially normally incident light and for the first polarization state, the light transmittance of the reflective polarizer comprises a second band edge separating a third wavelength range and a fourth wavelength range, the third wavelength range spanning at least about 450 nm to about 900 nm and the fourth wavelength range spanning at least about 1100 nm to about 1300 nm, and the reflective polarizer has an average light transmittance of less than about 5% within the third wavelength range and an average light transmittance of more than about 80% within the fourth wavelength range.

14. 14. The reflective polarizer of claim 13, wherein the second band edge has a second band edge wavelength corresponding to about 50% light transmission along the second band edge, the second band edge wavelength being in the range of about 925 nm to about 1050 nm.

15. 15. The reflective polarizer of claim 13 or 14, wherein a best linear fit correlating the optical transmittance to wavelength over at least the wavelength range over which the optical transmittance increases from about 10% to about 70% for the second band edge has a slope greater than about 2% / nm and an r-squared value greater than about 0.9.

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